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Thread: engine head parts-cast iron recommendation

  1. #31
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    Quote Originally Posted by mtraven View Post
    While I really appreciate the help in finding replacements and will pursue those, I am a bit thrown by the discouragement to make them myself. This is a machinist forum right, we make stuff, no? I have found a plug that would probably work with some machining, though that machining is harder to do now that its cut down to size and 3 of them will cost be $200 bucks & a couple of weeks...then I still have to machine them.... I can probably machine from scratch them by tuesday for like $20 in materials (still undecided). Also, the originals were the main point of failure & caused a lot of damage to my engine, so I am not dying to put those in.

    I am leaning towards stainless steel for the replacements (303 or 17-4) and would like to hear some opinions on material selection


    ps did anyone look at the photos I posted of the prototype replacement?
    If you can source chuck of Nimonic 80, Hastelloy or Inconel go ahead and make your own. IMO bigger problem than nasty machinability is the availability for home shop guy..

  2. #32
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    Quote Originally Posted by MattiJ View Post
    If you can source chuck of Nimonic 80, Hastelloy or Inconel go ahead and make your own. IMO bigger problem than nasty machinability is the availability for home shop guy..
    hastelloy & inconel are available from mcMaster-carr, though i'd be looking at 4-5x the cost of 17-4 ss.

    in trying to determine what the existing one is made of, I scrubbed in with every nasty solvent I could find, left it wet with water to see if it would rust....it did not...at all, not even the spot I hit with a file to test hardness(its not very hard at all). It also has a yellow patina that I have seen on heated SS but that I don't usually see on carbon steel without any rust. So I think I can rule out cast iron & carbon steel on account of the rust(lack there off). I think it was probably a SS, but I'm not sure if there are steel alloys, outside the SS class, that do no rust, for example, can inconel rust? Its high chromium & nickle and very little iron content makes me think it would not rust. hence the OEM part could have been that? One more detail, it is strongly attracted to a magnet.

    so summarize, the mystery metal is:

    -strongly attracted to a mag
    -does not rust
    -file bites in easily


    whats your guess?
    "it is no measure of mental health to be well adjusted to a profoundly sick society." -- krishnamurti
    "look deep into nature, and then you will understand everything better." -- albert einstien
    "any intelligent fool can make things bigger and more complex...It takes a touch of genius - and a lot of courage to move in the opposite direction."

  3. #33
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    Ferritic stainless steel
    Mark

  4. #34
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    May be what we in the UK call 400 series stainless which is a ferritic. Try a search for 420 stainless, I used to buy this from "Cru-Steel" an American company with a UK outlet. I would love to see a good picture of the inside of the part you intend to make, I was put off attempting to make Land Rover ones some years ago due to the cast spikes on the inner surface. Maybe the ones you are doing don't have the spikes ?

  5. #35
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    17-4 is also magnetic. I question what the continuous heat cycling will do to any of the ferric or precipitation hardening stainless. Were you thinking of heat treating it? If so.. to what?.

    One reason it many have been listed as "non serviceable" is that they could have been made oversize and cooled in liquid Nitrogen for a shrink fit. Nothing you can't do at home with a little pre-planning.

  6. #36
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    Default finished replacments

    well after a long process I finally finished the replacement precups. They are cut from 17-4 SS. I did not harden them, as the 20 year old original was not hard at all. As for the fit, the original was not even tight enough to stay in during assembly. I know people may say it was worn, but once clean, there remained circular machining marks indicating the original surface is still more or less present. As for the fit of the replacement, I went will a 0.001" interference fit, tapped in with a mallet. The surface of the precup sits 0.0015-0.0035 proud of the cylinder head, such that they are clamped between the deck of the block & head. pictures of the production proccess can be viewed here.


    I have reassembled the engine & it is running better than it has in many years. So I wanted to thank you all for your help in identifying the problem & guiding the manufacturing of the new ones, I really could not have done it without you!


    During this whole thing, I had a lot of time to think about how the initial parts were destroyed, this is my working theory:

    -the original parts were a ferritic SS, forged into shape & then turned - I imagine forging creates irregular internal stresses
    -I found the glow plugs I replaced a few years ago were 0.020" longer than the originals and were creating mechanical pressure on the precup.
    -during the year before the teardown, the engine was more difficult to start, leading to grossly excessive use of the glow plugs
    -about a month before the teardown, I found 2 of my injectors had broken springs, from what I've read, this causes dripping which leads to fast cooling & more internal stress.


    so let me know what you think of my work and thanks again for all your help.
    "it is no measure of mental health to be well adjusted to a profoundly sick society." -- krishnamurti
    "look deep into nature, and then you will understand everything better." -- albert einstien
    "any intelligent fool can make things bigger and more complex...It takes a touch of genius - and a lot of courage to move in the opposite direction."

  7. #37
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    Quote Originally Posted by Chris Evans View Post
    May be what we in the UK call 400 series stainless which is a ferritic. Try a search for 420 stainless, I used to buy this from "Cru-Steel" an American company with a UK outlet. I would love to see a good picture of the inside of the part you intend to make, I was put off attempting to make Land Rover ones some years ago due to the cast spikes on the inner surface. Maybe the ones you are doing don't have the spikes ?
    the only thing I had similar was an indexing tab on the OD of the part, not terribly difficult to replicate. The trickiest part by far was machining the port itself. I had to rotate the part with a significant offset for the one edge & then move vertically(wrt the cutter) for the other edge. There was very little room to make "rough cuts" everything was pretty much a final cut. I also did the entire thing on the lathe, I imagine several steps would be a easier on a mill, my mill doesn't plunge for ****, hence the lathe work.
    "it is no measure of mental health to be well adjusted to a profoundly sick society." -- krishnamurti
    "look deep into nature, and then you will understand everything better." -- albert einstien
    "any intelligent fool can make things bigger and more complex...It takes a touch of genius - and a lot of courage to move in the opposite direction."

  8. #38
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    Well, I'm impressed. Well done.

  9. #39
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    Somehow I find it very hard to believe that the parts just vanished from inside the engine. There would be a ****load of dents on piston and cylinder head in best case, more probably total destruction.
    Someone forgot or intentionally didn't previously install those cups.

  10. #40
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    Quote Originally Posted by mtraven View Post
    -I found the glow plugs I replaced a few years ago were 0.020" longer than the originals and were creating mechanical pressure on the precup.
    -during the year before the teardown, the engine was more difficult to start, leading to grossly excessive use of the glow plugs
    -about a month before the teardown, I found 2 of my injectors had broken springs, from what I've read, this causes dripping which leads to fast cooling & more internal stress.
    I'm not sure about interference being a mechanical stress problem, but if the end of a plug were touching the cup this may have acted as a heat sink preventing the glow plug from getting hot enough to assist in igniting the fuel. There could have been isolated hot spots where the glow plugs contacted the cups if the plugs were activated too long, but in my experiance the glow plugs quickly burn out if used to excess. As for the injectors, yes, a bad spray pattern can lead to all sorts of problems.

    Congratulations on a job well done. You have demonstrated exceptional mechanical skill sets and problem solving worthy of admiration. Very impressive!

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